Vehicles are often propelled by various types of internal combustion engines where the propulsion force is generated by expansion of hot combustion gases acting on pistons working in cylinders. The pistons in turn drive a crankshaft which is connected to the driving wheels by means of a gear box.
After connection of the crankshaft to the wheels using a suitable transmission ratio or xe2x80x9cgearxe2x80x9d the velocity of the vehicle is controlled by means of an accelerator influencing the rotational speed (rpm) of the engine. The function of the accelerator is to act as a fuel supply control for the amount of fuel (for instance Diesel engines) or fuel air mixture (for instance gasoline engines) that is supplied to the engine and thus generating various engine torque which in combination with the vehicle""s resistance to movement and its inertia determine the resulting engine speed and vehicle velocity. Sometimes the accelerator is connected to a regulator that strives to control the rpm of the engine to a value that corresponds to a set value that depends on the actuation of the accelerator. Most often such active control is not used but the resulting velocity of the vehicle caused by a certain actuation of the accelerator depends on the encountered resistance.
The power of an engine is strongly dependent of its rpm and engine torque is limited. Consequently, there is a need for varying the transmission ratio according to circumstances. For instance a lower transmission ratio is used to obtain enough force to climb a steep hill and high transmission ratios are used at high vehicle velocities to prevent the engine rpm from becoming too high. Every driver develops his/her own style and feeling for when and how to use which gear.
The transmission ratio can also be chosen by the program of a so called automatic gear box without the driver having to make decisions. The final speed of the vehicle is then determined by the position of the accelerator. In case of small actuation of the accelerator, the engine power is not sufficient for the use of a high transmission gear ratio and the automatic gear box chooses a smaller gear ratio. In case of large actuation, the engine power is sufficient also for high gear ratios, and after an acceleration period, the velocity of the vehicle will be high.
The program of automatic gear boxes may then be arranged in different ways so that changes to higher gear ratios take place at different engine rpm""s. When changes take place at high engine rpm""s close to the maximum engine power, the capacity of the engine is used to its maximum and acceleration can be high. If changes in gear ratio take place at lower engine rpm""s, the engine capacity is not fully exploited and acceleration is more gentle. With many automatic gear boxes, it is possible to choose between different programs for the achievement of different degrees of xe2x80x9csports car behaviorxe2x80x9d of the gear box. In some cases an automatic change to lower gear xe2x80x9cso called kick-downxe2x80x9d takes place when the accelerator is rapidly actuated.
From energy efficiency and fuel consumption points of view, operation at high engine RPM is decidedly unfavorable. Gas velocities at entrance and exit of the cylinders increase at increased rpm, causing increased flow-losses. Thus, over most of the operational range, for a given power output, the energy efficiency of an internal combustion engine gets better the lower the rpm is. When designing automatic transmission gear boxes, it constitutes a problem to adapt the gear choosing program to obtain both as good engine energy efficiency and as high power from the engine as possible.
The present invention provides a solution to the conflict between engine power utilization and efficiency for a system with automatic transmission so that the driver can all the time adjust this optimization according to circumstance. At all times the driver automatically chooses between fuel consumption and xe2x80x9csports carxe2x80x9d behavior in such a manner that at one moment he may give priority of the one and at the next moment to the other all according to the traffic situation.
The system is most easily described and at its best when operating in connection with a gear box having a continuously variable gear ratio. During normal conditions, already accelerated to cruising speed, the function then is as follows:
The engine control mechanism is set at maximum throttle or fuel supply. This control mechanism then determines neither the engine rpm nor the engine power or the vehicle velocity. Instead these entities are determined indirectly by the driver using a speed controller that regulates the gear box instead of the engine. When the gear ratio is decreased, the engine rpm increases and so does the engine power and the vehicle velocity. When instead the gear ratio is increased, the engine can no longer sustain its rpm, which decreases as does the engine power and the velocity.
Upon acceleration, the gear ratio is decreased, resulting in more engine output. The lower the gear ratio is set, the higher the rpm and the higher the engine power will be, and the more sporty the acceleration up to the maximum power rpm level, which is determined by the individual engine""s design characteristics.